Folding knives and tools suitable for many purposes are well known in the art. For example, U.S. Pat. No. 1,030,058 to Doles, U.S. Pat. No. 1,189,005 to Seely, U.S. Pat. No. 2,188,762 to Schrade, U.S. Pat. No. 3,868,774 to Miori, U.S. Pat. No. 4,233,737 to Peohlmann, U.S. Pat. No. 4,240,201 to Sawby et al., U.S. Pat. No. 4,274,200 to Coder, U.S. Pat. No. 4,451,982 to Collins, U.S. Pat. No. 4,502,221 to Pittman, U.S. Pat. No. 4,670,984 to Rickard, U.S. Pat. No. 4,837,932 to Elsener, U.S. Pat. No. 4,896,424 to Walker, U.S. Pat. No. 5,060,379 to Neely, U.S. Pat. No. 5,425,175 to Rogers, and U.S. Pat. No. 5,461,786 to Miller are representative of the available prior art.
As disclosed in several of the aforementioned patents, there are many different mechanisms for locking tool blades in an open position. For example, the patents to Sawby et al., Miller and Seely each disclose a variation of a “lock back” mechanism. This construction entails forming a notch on a tang of the blade which is engaged by a lug located on the spine of the knife to lock the blade in an open position. A shortcoming of this type of mechanism is that excessive wear can cause the locking mechanism to fail, thereby rendering the knife unsafe for use.
The patents to Neely and Collins each disclose another type of locking mechanism. As disclosed in these patents, a blade has a tang that is engaged by a member to prevent the blade from rotating from its open position. For example, in Collins, a slidable bolt is biased towards the tang to lock the blade in its open position. A shortcoming with Collins's knife construction is that the bolt is generally parallel with the blade, and the mechanism depends on the spine of the handle for strength. Neely's knife suffers from the same disadvantage as Collins's, and from the fact that the blade may be unlocked inadvertently by pulling the blade axially away from the handle during a normal cutting motion of the knife.
What is needed, then, is a stronger lock mechanism than has previously been available for holding a blade of a folding tool in an open, or extended, position, yet which is capable of being manufactured at a reasonable cost.